A concrete structure such as a road bridge has so far been considered as a semi-permanent structure. There is however posed a problem in strength because factors such as a long time use, increase in the volume of traffic, and increase in the live load on automobiles have caused considerable deterioration of concrete surface and cracks. A counter-measure against this problem is to reinforce a concrete structure, and it is a common practice for this purpose to reinforce the same with carbon fibers impregnated with a resin.
This reinforcing method comprises sticking reinforcing fibers such as carbon fibers impregnated with a resin onto the concrete surface, and hardening the reinforcing fibers by causing setting of the resin, thereby forming a reinforcing material enhanced with fibers, i.e., forming a fibre-reinforced composite material (FRP). According to this practice, it is possible to reinforce the concrete structure with a high reinforcing effect since the reinforcing fibers in the reinforcing material firmly adhering to the concrete surface serve as a tension material through a high tensile strength thereof.
The reinforcing fibers used for such reinforcing purposes are applicable in the form of a reinforcing fiber sheet impregnated, upon use, with a resin, in which the reinforcing fibers are arranged in a single direction or in two directions through an adhesive layer on a support sheet, or in the form of a prepreg of a flexible sheet semi-hardened by previously impregnating the reinforcing fibers arranged in a single direction or in two directions with a resin.
When reinforcing a concrete structure such as, for example, a concrete slab of a road bridge, with reinforcing fibers serving as a tension material, the center portion is reinforced by sticking the reinforcing fibers impregnated with a resin onto the lower surface, since there occurs a moment tending to produce a downward convexity at the center portion thereof. In a protruding portion of the slab, on the other hand, a moment in a direction counter to that at the center portion is produced. It is therefore necessary to reinforce the slab from the upper surface.
Reinforcing from the upper surface is accomplished by removing asphalt placed on the concrete slab to expose the upper surface, sticking the reinforcing fibers impregnated with a resin to the upper surface, hardening the same, and then, placing asphalt onto the thus formed reinforcing material.
This practice is however defective in that it is impossible to ensure a high adhesivity between the reinforcing material and the placed asphalt, resulting in displacement of asphalt upon passage of an automobile.
A concrete slab other than a road bridge slab, i.e., a parking lot slab or a warehouse slab, is used in some cases by placing asphalt on the slab concrete surface. When reinforcing the upper surface of such a slab having asphalt placed thereon with reinforcing fibers, a problem is again that a sufficient adhesivity is unavailable between the reinforcing material based on the reinforcing fibers and asphalt. In a concrete floor surface having asphalt placed thereon for the purpose of achieving simplified waterproofing on a roof of a building as well, there is posed the problem of unavailability of a satisfactory adhesivity between the reinforcing material using reinforcing fibers and asphalt.